Data storage devices are divided, for the most part, into volatile data storing devices that lose all recorded data when power is turned off and non-volatile data storing devices that keep data even when the power is turned off. Non-volatile data storing devices include hard disk drives (HDDs) and non-volatile random access memory (RAM). The HDDs include a read and write head and a rotating data recording medium and can store data of 100 Gb or more. However, a device that has rotating parts like the HDD wears over time and, thus, there is a high possibility of operational failure, thereby reducing reliability and life.
Research and development continues with respect to non-volatile data storage devices which do not have physically moving parts and can be fabricated of high density. One such device employs movement of a magnetic domain and magnetic domain walls within a magnetic substance, and is presently commonly referred to as “racetrack magnetic memory”. Regardless, a magnetic domain in such devices constitutes a minute magnetic region of ferromagnetic material, and has a common magnetic moment throughout the domain. The size and magnetization direction of a magnetic domain can be appropriately controlled by the shape, size, and properties of a magnetic substance and external energy. A magnetic domain wall is a boundary portion between immediately adjacent magnetic domains. Magnetic domains and their associated walls can be moved by an external magnetic field or by a current applied to a magnetic substance. Conceptually, a sequence of magnetic domains can be stored along a thin, narrow strip, and can be collectively moved along the strip. The magnetic domains and walls in the individual strips are caused to be moved past read and/or write heads to read the present state of the magnetization direction of the domains, and/or to change such with the write head.
Ideally, to have a predictable reading and writing of the respective domains, the domains should be placed at regular intervals along the strip and move in a discrete regular manner. Accordingly, a critical issue is to control the position of the magnetic domains and to move them in a controlled way. Further, the magnetic domains should not move or wander between read and write operations, for example due to thermal effects. Accordingly, pinning mechanisms have been developed to pin the domain walls from moving unless so-directed. Example manners of forming domain wall pinning sites includes provision of notches along the strip that comprises the magnetic material and/or implanting a species in localized spots within the magnetic material of individual strips.